Polyester-Based Coating Composition for Metal Substrates

ABSTRACT

The present invention provides novel packaging articles, e.g., food and beverage cans, having a novel coating composition applied to at least a portion of a surface thereon. In preferred embodiments, the coating composition includes at least a film-forming amount of a copolyester resin having a backbone that includes one or more soft segments and a plurality of hard segments. The copolyester resin preferably has a glass transition temperature from about from about 10° C. to about 50° C. The present invention also provides a method for making coated articles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/393,584 filed by Prouvost et al. on Oct. 15, 2010 and entitled“Polyester-Based Coating Composition for Metal Substrates,” which isincorporated by reference herein in its entirety.

BACKGROUND

A wide variety of coatings have been used to coat the surfaces oftwo-piece food and beverage cans. These cans are generally coated using“coil coating” operations, i.e., a planar sheet of a suitable metalsubstrate (e.g., steel or aluminum metal) is coated with a suitablecomposition and cured and then the coated substrate is formed into thecan end or body. The coating should be capable of high-speed applicationto the substrate and provide the necessary properties when cured toperform in this demanding end use. For example, the coating should besafe for food contact; have excellent adhesion to the substrate; becapable of being drawn during the forming step; when used as an endcoating, provide clean edges when the end is opened; resist staining andother coating defects such as “popping,” “blushing” and/or “blistering;”and resist degradation over long periods of time, even when exposed toharsh environments. Previous coatings have suffered from one or moredeficiencies.

Various coatings have been used as interior protective can coatings,including epoxy-based coatings and polyvinyl-chloride-based coatings.Each of these coating types, however, has potential shortcomings. Forexample, the recycling of materials containing polyvinyl chloride orrelated halide-containing vinyl polymers can be problematic. There isalso a desire by some to reduce or eliminate certain epoxy compoundscommonly used to formulate food-contact epoxy coatings.

To address the aforementioned shortcomings, the packaging coatingsindustry has sought coatings based on alternative binder systems such aspolyester resin systems. It has been problematic, however, to formulatepolyester-based coatings that exhibit the required balance of coatingcharacteristics (e.g., flexibility, adhesion, corrosion resistance,stability, resistance to crazing, etc.). For example, there hastypically been a tradeoff between corrosion resistance and fabricationproperties for such coatings. Polyester-based coatings suitable forfood-contact that have exhibited both good fabrication properties and anabsence of crazing having tended to be too soft and exhibit unsuitablecorrosion resistance. Conversely, polyester-based coatings suitable forfood contact that have exhibited good corrosion resistance havetypically exhibited poor flexibility and unsuitable crazing whenfabricated.

What is needed in the marketplace is an improved binder system for usein coatings such as, for example, packaging coatings. Such packages,compositions and methods for preparing the same are disclosed andclaimed herein.

SUMMARY

In one aspect, the present invention relates to a coating compositionuseful in a variety of coating applications. The coating compositionpreferably includes at least a film-forming amount of a polyesterpolymer, preferably in the form of a copolyester resin having a backbonethat includes one or more soft segments and one or more hard segments,and more preferably at least two hard segments. In preferredembodiments, the polyester polymer includes a plurality of hard segmentsand preferably has a glass transition temperature (“Tg”) of from about10° C. to about 50° C., more preferably from 10° C. to 35°. The one ormore hard segments preferably have a Tg from about 10° C. to about 100°C.

In one embodiment, the polyester polymer has the following structure:

(R¹)_(r)-([HARD]-X_(s)-[SOFT]-X_(s))_(n)—(R²)_(r)

wherein:

-   -   [HARD] independently denotes a hard segment;    -   [SOFT] independently denotes a soft segment;    -   each X, if present, is independently a divalent organic group;    -   each s is independently 0 or 1;    -   n is at least 1 (more preferably at least 2);    -   R¹, if present, is a reactive functional group, an organic        group, or a soft segment that may optionally include a terminal        reactive functional group and may optionally be connected to a        hard segment via a step-growth linkage;    -   R², if present, is a reactive functional group, an organic        group, or a hard segment that may optionally include a terminal        reactive functional group; and    -   each r is independently 0 or 1.

In one embodiment, the polyester polymer is a copolyester resin having aTg from 10° C. to 50° C. and including alternating hard and softsegments. The copolyester resin is preferably a reaction product ofingredients including: (i) a polyester oligomer or polymer (preferablyhydroxyl-terminated) having a Tg from 10° C. to 100° C. and (ii) an acidor polyacid (preferably a diacid) or equivalent (e.g., anhydride, esterand the like). Preferably, the hard segments are provided by ingredient(i) and the soft segments are provided by ingredient (ii).

Preferred coating compositions of the present invention aresubstantially free of mobile bisphenol A (“BPA”) and/or aromaticglycidyl ether compounds, e.g., diglycidyl ethers of BPA (“BADGE”),diglycidyl ethers of bisphenol F (“BFDGE”) and epoxy novalacs (e.g.,NOGE), and more preferred compositions are also substantially free ofbound BPA and/or aromatic glycidyl ether compounds.

The present invention also provides coated articles such as, forexample, packaging articles (e.g., food and beverage containers or aportion thereof). Preferred packaging articles include “two-piece” cansformed at least in part using a metal substrate. These preferred canstypically comprise a body portion and an end portion, wherein at leastone of the body and end portions are metal (e.g., aluminum or steel) andare coated on at least one major surface with a coating composition ofthe present invention.

The present invention also provides a method comprising: providing acoating composition of the present invention, which is preferablysuitable for use as a food-contact packaging coating when suitablycured, and applying the coating composition to at least a portion of aplanar metal substrate suitable for use in forming a food or beveragecontainer or a portion thereof. In preferred embodiments, this method isaccomplished utilizing a coil coating method. For example, a coil of asuitable substrate (e.g., aluminum or steel sheet metal) is first coatedwith the coating composition of the present invention on one or bothsides, cured (e.g., using a bake process), and then the cured substrateis formed (e.g., by stamping or drawing) into a food or beveragecontainer or a portion thereof such as, e.g., a beverage can end.

The present invention also provides a method comprising the steps of:providing a body and an end, wherein at least one of the end and thebody is coated on at least one side with a coating composition of thepresent invention; filling the body with a product (e.g., a food orbeverage product); and attaching the end to the body.

The details of one or more embodiments of the present invention are setforth in the description below. Other features, objects, and advantagesof the present invention will be apparent from the description and fromthe claims.

SELECTED DEFINITIONS

Unless otherwise specified, the following terms as used herein have themeanings provided below.

As used herein, the term “organic group” means a hydrocarbon group (withoptional elements other than carbon and hydrogen, such as oxygen,nitrogen, sulfur, and silicon) that is classified as an aliphatic group,a cyclic group, or combination of aliphatic and cyclic groups (e.g.,alkaryl and aralkyl groups). The term “aliphatic group” means asaturated or unsaturated linear or branched hydrocarbon group, which caninclude optional elements other than carbon and hydrogen. This term isused to encompass alkyl, alkenyl, and alkynyl groups, for example. Theterm “cyclic group” means a closed ring hydrocarbon group that isclassified as a cycloaliphatic group or an aromatic group, both of whichcan include heteroatoms. The term cycloaliphatic group means an organicgroup that contains a ring that is not an aromatic group.

A group that may be the same or different is referred to as being“independently” something. Substitution is anticipated on the organicgroups of the compounds of the present invention. As a means ofsimplifying the discussion and recitation of certain terminology usedthroughout this application, the terms “group” and “moiety” are used todifferentiate between chemical species that allow for substitution orthat may be substituted and those that do not allow or may not be sosubstituted. Thus, when the term “group” is used to describe a chemicalsubstituent, the described chemical material includes the unsubstitutedgroup and that group with O, N, Si, or S atoms, for example, in thechain (as in an alkoxy group) as well as carbonyl groups or otherconventional substitution. Where the term “moiety” is used to describe achemical compound or substituent, only an unsubstituted chemicalmaterial is intended to be included. For example, the phrase “alkylgroup” is intended to include not only pure open chain saturatedhydrocarbon alkyl substituents, such as methyl, ethyl, propyl, t-butyl,and the like, but also alkyl substituents bearing further substituentsknown in the art, such as hydroxy, alkoxy, alkylsulfonyl, halogen atoms,cyano, nitro, amino, carboxyl, etc. Thus, “alkyl group” includes ethergroups, haloalkyls, nitroalkyls, carboxyalkyls, hydroxyalkyls,sulfoalkyls, etc. On the other hand, the phrase “alkyl moiety” islimited to the inclusion of only pure open chain saturated hydrocarbonalkyl substituents, such as methyl, ethyl, propyl, t-butyl, and thelike. As used herein, the term “group” is intended to be a recitation ofboth the particular moiety, as well as a recitation of the broader classof substituted and unsubstituted structures that encompasses the moiety.

The term “substantially free” of a particular mobile compound means thatthe compositions of the present invention contain less than 100 partsper million (ppm) of the recited mobile compound. The term “essentiallyfree” of a particular mobile compound means that the compositions of thepresent invention contain less than 10 ppm of the recited mobilecompound. The term “essentially completely free” of a particular mobilecompound means that the compositions of the present invention containless than 1 ppm of the recited mobile compound. The term “completelyfree” of a particular mobile compound means that the compositions of thepresent invention contain less than 20 parts per billion (ppb) of therecited mobile compound.

The term “mobile” means that the compound can be extracted from thecured coating when a coating (typically ˜1 mg/cm² (6.5 mg/in²) thick) isexposed to a test medium for some defined set of conditions, dependingon the end use. An example of these testing conditions is exposure ofthe cured coating to HPLC-grade acetonitrile for 24 hours at 25° C. Ifthe aforementioned phrases are used without the term “mobile” (e.g.,“substantially free of XYZ compound”) then the compositions of thepresent invention contain less than the aforementioned amount of thecompound whether the compound is mobile in the coating or bound to aconstituent of the coating.

The term “crosslinker” refers to a molecule capable of forming acovalent linkage between polymers or between two different regions ofthe same polymer.

The term “water-dispersible” in the context of a water-dispersiblepolymer means that the polymer can be mixed into water (or an aqueouscarrier) to form a stable mixture. For example, a mixture that separatesinto immiscible layers after being stored for 1 week at 120° F. (48.9°C.) is not a stable mixture. The term “water-dispersible” is intended toinclude the term “water-soluble.” In other words, by definition, awater-soluble polymer is also considered to be a water-dispersiblepolymer.

The term “dispersion” in the context of a dispersible polymer refers tothe mixture of a dispersible polymer and a carrier. The term“dispersion” is intended to include the term “solution.”

Unless otherwise indicated, a reference to a “(meth)acrylate” compound(where “meth” is bracketed) is meant to include both acrylate andmethacrylate compounds.

The term “polycarboxylic acid” includes both polycarboxylic acids andanhydride or esterified variants thereof.

The term “on,” when used in the context of a coating applied on asurface or substrate, includes both coatings applied directly orindirectly to the surface or substrate. Thus, for example, a coatingapplied to a primer layer overlying a substrate constitutes a coatingapplied on the substrate.

Unless otherwise indicated, the term “polymer” includes bothhomopolymers and copolymers (i.e., polymers of two or more differentmonomers). Similarly, unless otherwise indicated, the use of a termdesignating a polymer class such as, for example, “polyester” isintended to include both homopolymers and copolymers (e.g., copolyesterpolymers).

The terms “unsaturated” or “unsaturation” when used in the context of acompound refers to a compound that includes at least one non-aromaticdouble bond, typically a carbon-carbon double bond.

The term “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

The terms “preferred” and “preferably” refer to embodiments of thepresent invention that may afford certain benefits, under certaincircumstances. However, other embodiments may also be preferred, underthe same or other circumstances. Furthermore, the recitation of one ormore preferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the present invention.

As used herein, “a,” “an,” “the,” “at least one,” and “one or more” areused interchangeably. Thus, for example, a coating composition thatcomprises “an” additive can be interpreted to mean that the coatingcomposition includes “one or more” additives.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, 5, etc.). Furthermore, disclosure of a range intendedto be a specific disclosure of all subranges included within the broaderrange (e.g., 1 to 5 discloses 1 to 4, 1.5 to 4.5, 1 to 2, etc.).

DETAILED DESCRIPTION

The present invention provides a polyester polymer that, in preferredembodiments, is a copolyester polymer having both one or more hardsegments and one or more soft segments. The polyester polymer isparticularly useful as a binder polymer in adherent coatings for use onpackaging articles such as, for example, metal food or beveragecontainers. Thus, the present invention also provides a coatingcomposition that preferably includes at least a film-forming amount ofthe polyester polymer of the present invention. Typically, the coatingcomposition further includes one or more optional liquid carriers andone or more other optional ingredients such as a crosslinker, acatalyst, a pigment, etc.

Preferred compositions of the present invention are substantially freeof mobile bisphenol A (BPA) and aromatic glycidyl ether compounds (e.g.,diglycidyl ether of BPA (BADGE), the diglycidyl ether of bisphenol F(BFDGE), and epoxy novalacs), more preferably essentially free of mobileBPA and aromatic glycidyl ether compounds, even more preferablyessentially completely free of mobile BPA and aromatic glycidyl ethercompounds, and most preferably completely free of mobile BPA andaromatic glycidyl ether compounds. The coating composition is also morepreferably substantially free of bound BPA and aromatic glycidyl ethercompounds, more preferably essentially free of bound BPA and aromaticglycidyl ether compounds, even more preferably essentially completelyfree of bound BPA and aromatic glycidyl ether compounds, and mostpreferably completely free of bound BPA and aromatic glycidyl ethercompounds.

The polyester polymers of the present invention are typically formedfrom reactants that include one or more polyacid molecules and one ormore polyol molecules. In the various discussions of polyester reactionmethods and reactants included herein, it should be understood that insynthesizing the polyester, the specified acids may be in the form ofcarboxylic acids, anhydrides, esters (e.g., alkyl ester) or likeequivalent form. Some representative examples of polyacids and polyolsuseful in producing polyesters are provided below.

Suitable polyacids include adipic, azelaic, cyclohexane dicarboxylic,fumaric, isophthalic, maleic, phthalic, sebacic, succinic, terephthalicacids, anhydrides and ester variants thereof, and mixtures thereof.

Suitable polyol molecules include ethylene glycol, propylene glycol,butylene glycol, neopentyl glycol (“NPG”, though NPG is not preferred incertain embodiments), cyclohexane diol, cyclohexane dimethanol, hexanediol, substituted propane diols (e.g., 2-methyl, 1,3-propane diol),substituted butane diols, substituted pentane diols, substituted hexanediols, methylol cycloalkanes (e.g., dimethylol cyclobutane, isosorbide,etc.), diethylene glycol and triols, and mixtures thereof.

The glass transition temperature (“Tg”) of the polyester polymer canvary depending on a variety of factors including, for example, theperformance requirements of the intended end use. In certain end uses,such as food or beverage can coatings, and beverage can ends inparticular (e.g., beer or soda riveted can ends), the coatingcomposition preferably exhibits both good flexibility (e.g., goodfabrication for stamped or drawn articles) and good corrosion resistance(e.g., acceptable levels of retort resistance). In preferred suchembodiments, the polyester polymer exhibits a Tg of at least about 10°C., more preferably at least about 15° C., and even more preferably atleast about 20° C. Preferably, the polyester polymer exhibits a Tg ofless than about 50° C., more preferably less than about 35° C., and evenmore preferably less than about 30° C. In one embodiment, the polyesterpolymer has a Tg from about 10° C. to about 35° C. A protocol useful formeasuring the Tg of the polyester polymer via differential scanningcalorimetry is provided in the Test Methods Section.

The polyester polymer of the present invention may be a linear polymeror a branched polymer. Polymers that are predominantly linear arepresently preferred.

If desired, the polyester polymer of the present invention may includeone or more step-growth linkages other than ester linkages. Examples ofsuch linkages include amide, carbonate ester, ester, ether, urea,urethane, or combinations thereof. In one embodiment, the polyesterpolymer does not include any linkages (e.g., condensation linkages)other than ester linkages.

In preferred embodiments, a backbone of the polyester polymer includesboth one or more hard segments and one or more soft segments. Morepreferably, the backbone includes a plurality of hard segments (i.e.,≧2, ≧3, ≧4, etc.) in combination with at least one soft segment (e.g.,≧1, ≧2, ≧3, etc.). While not intending to be bound by any theory, it isbelieved that the hard segments of the polyester polymer contribute tothe excellent corrosion resistance of food-contact coatings formulatedusing the polyester polymer, including in food or beverage can retortprocesses at elevated temperature and pressure while contactingcorrosive food or beverage product. The one or more soft segments arebelieved to impart elasticity to such coatings and facilitatefabrication.

In certain preferred embodiments, the coating composition of the presentinvention may be applied to flat planar metal substrate (e.g., aluminumor steel coil) prior to fabrication of the coated metal substrate (e.g.,via stamping) into an article such as a riveted beverage can end. Thecoating composition of the present invention exhibits excellentfabrication (e.g., flexibility to accommodate stamping of a beverage endrivet and the extreme contours associated therewith) in such end uses,while still exhibiting excellent adhesion, corrosion resistance andretortability.

The hard and soft segments are preferably dispersed throughout thepolyester backbone, preferably in a non-random distribution. Inpreferred embodiments, the polyester polymer has a backbone thatincludes an alternating sequence of hard and soft segments. In suchembodiments, the alternating hard and soft segments are typicallyconnected to one another via step-growth linkages, more typicallycondensation linkages such as ester linkages. A representative exampleof such an alternating polymer is provided below in Formula I:

(R¹)_(r)-([HARD]-X_(s)-[SOFT]-X_(s))_(n)—(R²)_(r)

where:

-   -   [HARD] independently denotes a hard segment of the present        invention;    -   [SOFT] independently denotes a soft segment of the present        invention;    -   each X, if present, is independently a divalent organic group,        and more preferably a step-growth linkage such as, e.g., a        condensation linkage;    -   each s is independently 0 or 1, more preferably 1;    -   n is 1 or more, more preferably to 1 to 15;    -   R¹, if present, is a reactive functional group (e.g., —OH,        —COOH, etc.), an organic group, or a soft segment that may        optionally include a terminal reactive functional group;    -   R², if present, is a reactive functional group (e.g., —OH,        —COOH, etc.), an organic group or a hard segment that may        optionally include a terminal reactive functional group and may        optionally be connected to a hard segment via a divalent linkage        (typically a step-growth linkage); and    -   each r is independently 0 or 1.

In one embodiment, n is at least 2; each s is 1; each X is an esterlinkage; each r is 1; R¹ is a reactive functional group, more preferablya hydroxyl group; and R² is a hard segment terminated with a reactivefunctional group, preferably R² is a hydroxyl-terminated hard segment.

In some embodiments, the polyester polymer of the present invention isterminated on each end with a hard segment, more preferably a hardsegment having a terminal reactive functional group, and even morepreferably a hydroxyl-terminated hard segment.

In preferred embodiments, the ratio, on a weight basis, of hard to softsegments in the polyester polymer is on average from 1:1 to 50:1, morepreferably from 8:1 to 20:1, and even more preferably from 10:1 to 15:1(hard segments:soft segments).

The polyester polymer may include any number of hard and soft segments.In preferred embodiments, the polyester polymer includes, on average,from 1 to 35, more preferably from 2 to 20, and even more preferablyfrom 4 to 10 of each of the hard and soft segments. In preferredembodiments, the polyester polymer includes, on average, w soft segments(where “w” is the average number of soft segments) and w+1 hard segments(e.g., when w is 3, w+1 is 4).

The polyester polymer of the present invention may include one or moreoptional backbone segments (e.g., monomer, oligomer, or polymersegments) other than the hard or soft segments. Such optional segmentsmay be monomer, oligomer, and/or polymer segments. In some embodiments,however, the hard and soft segments constitute substantially all, oreven all, of the polyester polymer on a weight basis. In suchembodiments, the hard and soft segments preferably constitute at least75 weight percent (“wt-%”), at least 90 wt-%, at least 99 wt-%, or 100wt-% of the polyester polymer of the present invention. The above weightpercentages include any linkage groups (e.g., ester linkages) linkingthe hard and soft segments that are formed via reaction of complimentaryreactive functionalities (e.g., hydroxyl and carboxylic groups) presenton precursor hard and soft segment reactants.

The one or more hard segments of the polyester polymer are preferably anoligomer or polymer segment, and more preferably a polyester oligomer orpolymer segment or a combination thereof. The hard segment preferablyhas a number average molecular weight (Mn) of at least 500. In preferredembodiments, the one or more hard segments exhibit a Tg of at least 10°C., more preferably at least 15° C., and even more preferably at least20° C. Preferably, the one or more hard segments exhibits a Tg of lessthan about 100° C., more preferably less than 80° C., and even morepreferably less than 70° C. In a particularly preferred embodiment, thehard segment has a Tg of from 20° C. to 40° C. By Tg of the hard segmentis meant the Tg of the isolated component of the hard segment. Aprotocol useful for measuring the Tg of the hard segment viadifferential scanning calorimetry is provided in the Test Methodssection.

The one or more hard segments preferably include a suitable amount ofone or more of the following cyclic groups: aromatic groups (e.g., arylgroups, heteroaryl groups, or a combination thereof), saturated orunsaturated monocyclic alicyclic groups, saturated or unsaturatedpolycyclic groups (e.g., bicyclic groups or tricyclic or higherpolycyclic groups) that may include any combination of aromatic and/oralicyclic groups, or a combination thereof. Examples of suitablecompounds for incorporating cyclic groups into the hard segments includecyclohexane dicarboxylic acid, cyclohexane dimethanol, naphthalenedicarboxylic acid, diphenyl dicarboxylic acid, isoterephthalic acid,nadic anhydride, terephthalic acid, ortho-phthalic anhydride,isosorbide, tricyclodecanedimethanol, dimethylolcycloalkanes,combinations thereof, and variants (e.g., carboxylic, esterified, oranhydride variants) or derivatives thereof. Isoterephthalic acid andterephthalic acid are preferred cyclic-group-containing monomers for usein forming the one or more hard segments.

In some embodiments, the polymer includes at least one hard segmentwhere cyclic groups, and more preferably aromatic groups, constitute atleast 20 wt-%, more preferably at least 40 wt-%, even more preferably atleast 45 wt-%, and optimally at least 50 wt-% of the hard segment. Theupper concentration of cyclic groups in the hard segments is notparticularly limited, but preferably the amount of such groups isconfigured such that the Tg of the hard segment does not exceed the Tgranges previously discussed. The total amount of cyclic groups in thehard segment will typically constitute less than 100 wt-%, morepreferably less than about 90 wt-%, and even more preferably less than80 wt-% of the hard segment. The above weight percentages are expressedin terms of the total amount of cyclic-group-containing monomer presentin the hard segment. In some embodiments, all or substantially all ofthe one or more hard segments present in the polyester polymer includean amount of cyclic groups falling within the above weight percentages.

In certain preferred embodiments, the hard segments are formed using oneor more aromatic monomers, more preferably one or more aromaticpolyacids or anhydrides, with aromatic diacids or anhydrides beingespecially preferred. Preferred aromatic diacids or anhydrides includeortho-phthalic anhydride, isophthalic acid, terephthalic acid, andmixtures or derivatives thereof.

In some embodiments, one or more polyols may also be included in thehard segments to influence the Tg such that it is suitably high to fallwithin a desired Tg range. Preferred such polyols include methyl propanediol (i.e., MPdiol), neopentyl glycol, tricyclodecane dimethanol,isorbide, and combinations or derivatives thereof. In a presentlypreferred embodiment, the hard segment is formed from ingredientsincluding one or more such polyols in combination with one or morearomatic monomers (more preferably one or more aromatic diacids oranhydrides).

The hard segments may include substituents (either backbone or pendant)selected from, for example, oxygen atoms, nitrogen atoms, phosphorusatoms, sulfur atoms, silicon atoms, or groups containing any of theaforementioned atoms in combination with one or more atoms.

The hard segments may be of any suitable size. Preferably, the hardsegments have an Mn of at least 500, more preferably at least 750, andeven more preferably at least 1,000. Although the upper molecular weightof the hard segments is not particularly limited, in some embodiments,the hard segments exhibits an Mn of less than about 10,000, morepreferably less than about 8,000, and even more preferably less thanabout 5,000.

In preferred embodiments, hard segments constitute at least 55 wt-%,more preferably at least 65 wt-%, and even more preferably at least 75wt-% of the polyester polymer. In some embodiments, the hard segmentsconstitute less than about 98 wt-%, more typically less than about 95wt-%, and even more typically less than about 92 wt-% of the polyesterpolymer. The above weight percents refers to the non-volatile weight ofthe ingredients used to generate the one or more hard segments relativeto the total non-volatile weight of the ingredients used to generate thepolyester polymer.

The one or more soft segments can be of any suitable segment length andmay be polymer segments, oligomer segments, monomer segments, or acombination thereof. When the one or more soft segments are polymerand/or or oligomer segments, polyester segments are preferred. The softsegments are preferably at least substantially aliphatic and morepreferably are completely aliphatic (i.e., do not include any aromaticgroups). While the soft segment may include one or more cyclic groups(e.g., so long as the desired properties of the polymer are preserved),in some embodiments, the soft segment is a linear chain segment thatdoes not contain any aromatic groups, and more preferably does notcontain any cyclic groups.

In preferred embodiments, the soft segment is an organic group thatincludes at least 4 carbon atoms and more preferably at least 6 carbonatoms. The soft segment may include substituents (either backbone orpendant) selected from, for example, oxygen atoms, nitrogen atoms,phosphorus atoms, sulfur atoms, silicon atoms, or groups containing anyof the aforementioned atoms in combination with one or more atoms. In apresently preferred embodiment, the soft segment is an organic group,more preferably a divalent hydrocarbon group or moiety, which includesfrom 4 to 60 carbon atoms and more preferably from 6 to 36 carbon atoms.In such embodiments, the soft segment is typically derived from areactant having (i) 4 to 60 carbon atoms and (ii) at least one, and morepreferably two or more, reactive groups capable of participating in astep-growth reaction (more preferably a condensation reaction such as anester-forming condensation reaction). Preferred reactive groups includecarboxylic groups, anhydride groups, ester groups, and hydroxyl groups,with carboxylic groups being presently preferred.

In some embodiments, the soft segment is derived from a compound havingthe structure R³—(CR⁴ ₂)_(t)—R³, wherein: each R³ is independently areactive group capable of participating in a step-growth reaction suchas any of the preferred reactive groups discussed above; t is at least2, more preferably 4 to 60, even more preferably 6 to 36, and optimally8 to 36; and each R⁴ is independently a hydrogen, a halogen, or anorganic group. In one such embodiment, each R⁴ is hydrogen and each R³is a carboxylic group or equivalent thereof.

In a preferred embodiment, the soft segment is derived from a carboxyl-or hydroxyl-terminated aliphatic reactant. In some embodiments, thechain linking the terminal hydroxyl or carboxyl end groups is ahydrocarbon chain that does not include any backbone heteroatoms.

In some embodiments, such as when the Mn of the soft segment is low, itmay not be feasible to determine a Tg corresponding to the soft segment.However, since the measured Tg of a polymer tends to increase withmolecular weight, when direct measurement of the Tg of the one or moresoft segments is not feasible, information regarding the influence ofthe one or more soft segments on Tg may be gleaned by comparing the Tgof the one or more hard segments to the overall Tg of the polyesterpolymer. The material or materials used to generate the one or more softsegments are preferably selected such that the one or more soft segmentscontribute to (i) a lower overall Tg for the polyester polymer (e.g., ascompared to a polyester polymer of a similar molecular weight lackingthe one or more soft segments) and/or (ii) enhanced fabricationproperties (e.g., flexibility) for a coating composition formulatedusing the polyester polymer. Examples of materials for use in formingthe soft segment (either neat or in combination with one or morecomonomers) include adipic acid; azelaic acid; fatty acid-basedmaterials such as fatty acid dimers or dimer fatty diols (e.g., producedby hydrogenation of the corresponding diol); sebacic acid; succinicacid; glutaric acid; a derivative or variant thereof; or a mixturethereof. In some embodiments, a soft segment is derived from one of theabove monomers without the use of an additional comonomer. When the softsegment is a polyester oligomer or polymer, the aforementioned monomersmay be used in combination with one or more suitable comonomers togenerate the soft segment.

The soft segment is typically attached on at least one end, and morepreferably both ends, to another portion or portions of the polymer.While the soft segment may be attached to a segment of the polyesterpolymer other than a hard segment, typically the soft segment isattached on one or both ends to a hard segment or segments via a linkagegroup. Although not presently preferred, it is contemplated that thesoft segment may be a backbone terminal group. Typically, the softsegment is attached on one or both ends to another portion or portionsof the polymer via a step-growth linkage such as, for example, acondensation linkage. Examples of step-growth linkages include amide,carbonate ester, ester, ether, urea, or urethane linkage, with esterlinkages being preferred. In a preferred embodiment, the polyesterpolymer of the present invention includes at least one backbone softsegment attached on each end via an ester linkage to a pair of hardsegments.

The polyester polymer of the present invention may be formed using anysuitable method. For example, the following methods may be employed invarious embodiments:

-   -   A preformed hard segment is reacted with a preformed soft        segment to form the polyester polymer.    -   The soft segment is formed in situ in the presence of a        preformed hard segment.    -   The hard segment is formed in situ in the presence of a        preformed soft segment.        A presently preferred method for forming the polyester polymer        of the present invention is to react a hydroxy-terminated        polyester oligomer or polymer comprising the hard segment with a        polycarboxylic acid (preferably a dicarboxylic acid or        equivalent) comprising the soft segment.

Preferred polyesters for use in solvent-based coating embodiments of thepresent invention have an acid number below about 10, more preferablybelow about 5 and most preferably about 4. The acid number (as used inreference to the present compositions) is the number of milligrams ofpotassium hydroxide required to neutralize one gram of the solidpolyacid polymer. The acid number of an anhydride-containing polymer isdetermined by initially hydrolyzing the anhydride-containing polymer toobtain the corresponding polyacid polymer. The acid number is thendetermined in the same manner as for a polyacid polymer.

Preferred polyesters for use in the present invention have a hydroxylnumber (OH number) below about 50, more preferably below about 40.Typically, the polyester polymer will have a hydroxyl number of at least10, more preferably at least 20. The hydroxyl number of ahydroxyl-containing polymer of the present invention is determined by:(i) esterifying the polymer with acetic anhydride and pyridine to obtainan esterified polymer and acetic acid; and (ii) then neutralizing theacetic acid with potassium hydroxide. The units are expressed similarlyto acid number, i.e., the number of milligrams of potassium hydroxiderequired to neutralize the acetic acid formed as described above per onegram of hydroxyl-containing polymer.

If water-dispersibility is desired, the polyester polymer of the presentinvention may contain a suitable amount of salt-containing and/orsalt-forming groups to facilitate preparation of an aqueous dispersionor solution. Suitable salt-forming groups may include neutralizablegroups such as acidic or basic groups. At least a portion of thesalt-forming groups may be neutralized to form salt groups useful fordispersing the polyester polymer into an aqueous carrier. Acidic orbasic salt-forming groups may be introduced into the polyester polymerby any suitable method.

Non-limiting examples of anionic salt groups include neutralized acid oranhydride groups, sulphate groups (—OSO₃ ⁻), phosphate groups (—OPO₃ ⁻),sulfonate groups (—SO₂O⁻), phosphinate groups (—POO⁻), phosphonategroups (—PO₃ ⁻), and combinations thereof. Non-limiting examples ofsuitable cationic salt groups include:

(referred to, respectively, as quaternary ammonium groups, quaternaryphosphonium groups, and tertiary sulfate groups) and combinationsthereof. Non-ionic water-dispersing groups (e.g., hydrophilic groupssuch as ethylene oxide groups) may also be used. Compounds forintroducing the aforementioned groups into polymers are known in theart.

In some embodiments, a water-dispersible polyester polymer is achievedthrough inclusion of a sufficient number of carboxylic acid groups inthe polymer. Examples of suitable materials for incorporating suchgroups into the polymer include polyanhydrides such astetrahydrophthalic anhydride, pyromellitic anhydride, succinicanhydride, trimellitic anhydride (“TMA”), and mixtures thereof. Thecarboxylic-functional polyester oligomer or polymer is at leastpartially neutralized (e.g., using a base such as an amine) to producean aqueous dispersion.

In some embodiments, it is contemplated that water-dispersibility may beprovided through use of acid-functional ethylenically unsaturatedmonomers that have been grafted onto the polyester (e.g., via inclusionof an unsaturated monomer in the polyester such as maleic anhydride) toform a polyester-acrylic copolymer, whereby a suitable number of theacid-functional groups are neutralized with base (such as, e.g., atertiary amine) to produce salt groups. See for example, U.S. Pat. App.No. 20050196629 for examples of such techniques.

In some embodiments, the polyester polymer (and preferably the coatingcomposition) is at least substantially “epoxy-free,” more preferably“epoxy-free.” The term “epoxy-free,” when used herein in the context ofa polymer, refers to a polymer that does not include any “epoxy backbonesegments” (i.e., segments formed from reaction of an epoxy group and agroup reactive with an epoxy group). Thus, for example, a polymer havingbackbone segments that are the reaction product of a bisphenol (e.g.,bisphenol A, bisphenol F, bisphenol S, 4,4′dihydroxy bisphenol, etc.)and a halohdyrin (e.g., epichlorohydrin) would not be consideredepoxy-free. However, a vinyl polymer formed from vinyl monomers and/oroligomers that include an epoxy moiety (e.g., glycidyl methacrylate)would be considered epoxy-free because the vinyl polymer would be freeof epoxy backbone segments.

In some embodiments, the polyester polymer of the present invention is“PVC-free,” and preferably the coating composition is also “PVC-free.”That is, each composition preferably contains less than 2 wt-% of vinylchloride materials, more preferably less than 0.5 wt-% of vinyl chloridematerials, and even more preferably less than 1 ppm of vinyl chloridematerials.

Preferred coating compositions include at least about 60 wt-%, morepreferably at least about 65 wt-%, and even more preferably at leastabout 70 wt-% of the polyester polymer of the present invention.Preferred coating compositions include up to about 100 wt-%, morepreferably up to about 95 wt-%, and even more preferably up to about 80wt-% of the polyester polymer of the present invention. These weightpercentages are based on the total weight of resin solids present in thecoating composition.

In accordance with the present invention, the coating compositionfurther comprises a crosslinking resin in preferred embodiments. Forexample, any of the well known hydroxyl-reactive curing resins can beused. The choice of particular crosslinker typically depends on theparticular product being formulated. Non-limiting examples of suitablecrosslinkers include aminoplasts, phenoplasts, blocked isocyanates, andcombinations thereof.

Phenoplast resins include the condensation products of aldehydes withphenols. Formaldehyde and acetaldehyde are preferred aldehydes. Variousphenols can be employed such as phenol, cresol, p-phenylphenol,p-tert-butylphenol, p-tert-amylphenol, and cyclopentylphenol.

Aminoplast resins include, for example, the condensation products ofaldehydes such as formaldehyde, acetaldehyde, crotonaldehyde, andbenzaldehyde with amino- or amido-group-containing substances such asurea, melamine, and benzoguanamine Examples of suitable aminoplastresins include, without limitation, benzoguanamine-formaldehyde resins,melamine-formaldehyde resins, esterified melamine-formaldehyde, andurea-formaldehyde resins.

Condensation products of other amines and amides can also be employedsuch as, for example, aldehyde condensates of triazines, diazines,triazoles, guanadines, guanamines and alkyl- and aryl-substitutedmelamines Some examples of such compounds are N,N′-dimethyl urea,benzourea, dicyandimide, formaguanamine, acetoguanamine, glycoluril,ammelin 2-chloro-4,6-diamino-1,3,5-triazine,6-methyl-2,4-diamino-1,3,5-triazine, 3,5-diaminotriazole,triaminopyrimidine, 2-mercapto-4,6-diaminopyrimidine,3,4,6-tris(ethylamino)-1,3,5-triazine, and the like. While the aldehydeemployed is typically formaldehyde, other similar condensation productscan be made from other aldehydes, such as acetaldehyde, crotonaldehyde,acrolein, benzaldehyde, furfural, glyoxal and the like, and mixturesthereof.

Non-limiting examples of suitable isocyanate crosslinkers includeblocked or non-blocked aliphatic, cycloaliphatic or aromatic di-, tri-,or poly-valent isocyanates, such as hexamethylene diisocyanate (HMDI),cyclohexyl-1,4-diisocyanate and the like, and mixtures thereof. Furthernon-limiting examples of generally suitable blocked isocyanates includeisomers of isophorone diisocyanate, dicyclohexylmethane diisocyanate,toluene diisocyanate, diphenylmethane diisocyanate, phenylenediisocyanate, tetramethyl xylene diisocyanate, xylylene diisocyanate,and mixtures thereof. In some embodiments, blocked isocyanates are usedthat have an Mn of at least about 300, more preferably at least about650, and even more preferably at least about 1,000.

The level of curing agent required will depend on the type of curingagent, the time and temperature of the bake, and the molecular weight ofthe polymer. When used, the crosslinker is typically present in anamount ranging from between about 5 to 40% by weight. Preferably, thecrosslinker is present in an amount ranging from between 10 to 30% byweight; and more preferably, from between 15 to 25% by weight. Theseweight percentages are based upon the total weight of the resin solidsin the coating composition.

If desired, the coating composition may optionally include one or morevinyl polymers. An example of a preferred vinyl polymer is an acryliccopolymer, with acrylic copolymers having pendant glycidyl groups beingparticularly preferred. Suitable such acrylic copolymers are describedin U.S. Pat. No. 6,235,102, which is herein incorporated by reference.When present, the optional acrylic copolymer is typically present in anamount ranging from 2 to 20% by weight. Preferably, the acryliccopolymer is present in an amount ranging from between 2 to 15% byweight; more preferably, from between 2 to 10% by weight; and optimally,from between 5 to 10% by weight. These weight percentages are based uponthe total weight of the resin solids in the coating composition.

Suitable acrylic copolymers having pendant glycidyl groups that areuseful in the present invention preferably contain about 30 to 80 wt-%,more preferably about 40 to 70 wt-%, and most preferably about 50 to 70wt-% of a monomer containing a glycidyl group, for example, glycidylmethacrylate.

Suitable monomers containing a glycidyl group include any monomer havingan aliphatic carbon-carbon double bond and a glycidyl group. Typically,the monomer is a glycidyl ester of an alpha, beta-unsaturated acid, oranhydride thereof. Suitable alpha, beta-unsaturated acids includemonocarboxylic acids or dicarboxylic acids. Examples of such carboxylicacids include, but are not limited to, acrylic acid, methacrylic acid,alpha-chloroacrylic acid, alpha-cyanoacrylic acid, beta-methylacrylicacid (crotonic acid), alpha-phenylacrylic acid, beta-acryloxypropionicacid, sorbic acid, alpha-chlorosorbic acid, angelic acid, cinnamic acid,p-chlorocinnamic acid, beta-stearylacrylic acid, itaconic acid,citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleicacid, fumaric acid, tricarboxyethylene, maleic anhydride, and mixturesthereof. Specific examples of monomers containing a glycidyl group areglycidyl (meth)acrylate (i.e., glycidyl methacrylate and glycidylacrylate), mono- and di-glycidyl itaconate, mono- and di-glycidylmaleate, and mono- and di-glycidyl formate. It also is envisioned thatallyl glycidyl ether and vinyl glycidyl ether can be used as themonomer.

It also should be pointed out that the acrylic copolymer can initiallybe a copolymer of an alpha, beta-unsaturated acid and an alkyl(meth)acrylate, which then is reacted with a glycidyl halide ortosylate, e.g., glycidyl chloride, to position pendant glycidyl groupson the acrylate copolymer. The alpha, beta-unsaturated carboxylic acidcan be an acid listed above, for example.

In an alternative embodiment, an acrylic copolymer having pendanthydroxyl groups first is formed. The acrylic copolymer having pendanthydroxyl groups can be prepared by incorporating a monomer like2-hydroxyethyl methacrylate or 3-hydroxypropyl methacrylate into theacrylate copolymer. The copolymer then is reacted to position pendantglycidyl groups on the acrylic copolymer.

A preferred monomer containing a glycidyl group is glycidyl(meth)acrylate.

The acrylic copolymer may optionally be formed from reactants includingan alkyl (meth)acrylate having the structure: CH₂═C(R⁵)—CO—OR⁶ whereinR⁵ is hydrogen or methyl, and R⁶ is an alkyl group containing 1 to 16carbon atoms. The R⁶ group can be substituted with one or more, andtypically one to three, moieties such as hydroxy, halo, amino, phenyl,and alkoxy, for example. Suitable alkyl (meth)acrylates for use in thecopolymer therefore encompass hydroxy alkyl (meth)acrylates andaminoalkyl (meth)acrylates. The alkyl (meth)acrylate typically is anester of acrylic or methacrylic acid. Preferably, R⁵ is methyl and R⁶ isan alkyl group having 2 to 8 carbon atoms. Most preferably, R⁵ is methyland R⁶ is an alkyl group having 2 to 4 carbon atoms. Examples of thealkyl (meth)acrylate include, but are not limited to, methyl, ethyl,propyl, isopropyl, butyl, isobutyl, pentyl, isoamyl, hexyl,2-aminoethyl, 2-hydroxyethyl, 2-ethylhexyl, cyclohexyl, decyl, isodecyl,benzyl, 2-hydroxypropyl, lauryl, isobornyl, octyl, and nonyl(meth)acrylates.

The acrylic copolymer preferably comprises one or more vinyl comonomerssuch as styrene, halostyrene, isoprene, diallylphthalate,divinylbenzene, conjugated butadiene, alpha-methylstyrene, vinyltoluene, vinyl naphthalene, and mixtures thereof. Other suitablepolymerizable vinyl monomers include acrylonitrile, acrylamide,methacrylamide, methacrylonitrile, vinyl acetate, vinyl propionate,vinyl butyrate, vinyl stearate, isobutoxymethyl acrylamide, and thelike.

The aforementioned monomers may be polymerized by standard free radicalpolymerization techniques, e.g., using initiators such as peroxides orperoxy esters, to provide an acrylic copolymer preferably having an Mnof about 2,000 to 15,000, more preferably about 2,500 to 10,000, andmost preferably about 3,000 to 8,000. The acrylic may be produced insitu in presence of the polyester polymer and/or may be least partiallygrafted to the polyester (e.g., if the polyester contains unsaturationsuch as may be introduced using maleic anhydride).

The coating composition of the present invention may also include otheroptional ingredients that do not adversely affect the coatingcomposition or a cured coating composition resulting therefrom. Suchoptional ingredients are typically included in a coating composition toenhance composition esthetics, to facilitate manufacturing, processing,handling, and application of the composition, and to further improve aparticular functional property of a coating composition or a curedcoating composition resulting therefrom.

Such optional ingredients include, for example, catalysts, dyes,pigments, toners, extenders, fillers, lubricants, anticorrosion agents,flow control agents, thixotropic agents, dispersing agents,antioxidants, adhesion promoters, light stabilizers, and mixturesthereof. Each optional ingredient is included in a sufficient amount toserve its intended purpose, but not in such an amount to adverselyaffect a coating composition or a cured coating composition resultingtherefrom.

One optional ingredient is a catalyst to increase the rate of cureand/or the extent of crosslinking. Non-limiting examples of catalysts,include, but are not limited to, strong acids (e.g., dodecylbenzenesulphonic acid (DDBSA, available as CYCAT 600 from Cytec), methanesulfonic acid (MSA), p-toluene sulfonic acid (pTSA), dinonylnaphthalenedisulfonic acid (DNNDSA), and triflic acid), quaternary ammoniumcompounds, phosphorous compounds, tin and zinc compounds, andcombinations thereof. Specific examples include, but are not limited to,a tetraalkyl ammonium halide, a tetraalkyl or tetraaryl phosphoniumiodide or acetate, tin octoate, zinc octoate, triphenylphosphine, andsimilar catalysts known to persons skilled in the art. If used, acatalyst is preferably present in an amount of at least 0.01 wt-%, andmore preferably at least 0.1 wt-%, based on the weight of nonvolatilematerial in the coating composition. If used, a catalyst is preferablypresent in an amount of no greater than 3 wt-%, and more preferably nogreater than 1 wt-%, based on the weight of nonvolatile material in thecoating composition.

Another useful optional ingredient is a lubricant, like a wax, whichfacilitates manufacture of coated articles (e.g., food or beverage canends) by imparting lubricity to planar coated metal substrate. Alubricant is preferably present in the coating composition in an amountof 0 to about 2%, and preferably about 0.1 to about 2%, by weight ofnonvolatile material. Preferred lubricants include, for example,Carnauba wax and polyethylene type lubricants.

Another useful optional ingredient is a pigment, like titanium dioxide.A pigment, like titanium dioxide, is optionally present in the coatingcomposition in an amount of 0 to about 50%.

In preferred embodiments, the coating composition is a liquidcomposition, where the resins, crosslinker and other optionalingredients are dispersed in a liquid carrier. Any suitable carrier maybe used to prepare the coating composition. Suitable carriers includeorganic solvents, water, and mixtures thereof. Preferably, the carriers)are selected to provide a dispersion or solution of the polyesterpolymer of the present invention for further formulation. In certainpreferred embodiments, the carrier is a nonaqueous carrier. The carrierpreferably has sufficient volatility to evaporate essentially entirelyfrom the coating composition during the curing process, such as duringheating at about 220 to 260° C. for about 10 to 30 seconds.

Suitable nonaqueous carriers are known in the art of coatingcompositions, and include, for example, but are not limited to, glycolethers, like ethylene glycol monomethyl ether, ethylene glycol monoethylether, ethylene glycol monobutyl ether, and propylene glycol monomethylether; ketones, like cyclohexanone, ethyl aryl ketones, methyl arylketones, and methyl isoamyl ketone; aromatic hydrocarbons, like aromatic100, butyl cellosolve, toluene, benzene, and xylene; aliphatichydrocarbons, like mineral spirits, kerosene, and naphtha; alcohols,like isopropyl alcohol, n-butyl alcohol, and ethyl alcohol; aproticsolvents, like tetrahydrofuran; chlorinated solvents; esters (e.g.,dibasic ester); glycol ether esters, like propylene glycol monomethylether acetate; and mixtures thereof. It should be understood thatsolvent-based embodiments of the coating composition can include water(though this is not preferred), preferably at most a relatively lowamount of water, such as up to about 5% by total weight of thecomposition. The water can be added to the composition intentionally, orcan be present in the composition inadvertently, such as when water ispresent in a particular component included in the coating composition.

The amount of optional liquid carrier included in the composition islimited only by the desired, or necessary, rheological properties of thecomposition. Usually, a sufficient amount of carrier is included in thecoating composition to provide a composition that can be processedeasily and that can be applied to a metal substrate easily anduniformly, and that is sufficiently removed from the coating compositionduring curing within the desired cure time. Preferred coatingcompositions have between 10 to 50 wt-% solids, more preferably between20 to 40 wt-% solids.

In some water-based coating embodiments, the coating compositionpreferably includes at least about 10 wt-%, more preferably at leastabout 20 wt-%, and even more preferably at least about 25 wt-% of water,based on the total weight of the coating composition. In some suchembodiments, the coating composition preferably includes less than about90 wt-%, less than about 60 wt-%, less than about 50 wt-%, or less thanabout 40 wt-% of water, based on the total weight of the coatingcomposition.

In some embodiments, the cured coating composition of the presentinvention preferably has a Tg of at least 20° C., more preferably atleast 25° C., and even more preferably at least 30° C. Preferably, theTg of the coating composition is less than about 80° C., more preferablyless than about 70° C., and even more preferably less than about 60° C.

Cured coatings of the present invention preferably adhere well to metal(e.g., steel, tin-free steel (TFS), tin plate, electrolytic tin plate(ETP), aluminum, etc.) and provide high levels of resistance tocorrosion or degradation that may be caused by prolonged exposure toproducts such as food or beverage products. The coatings may be appliedto any suitable surface, including inside surfaces of containers,outside surfaces of containers, container ends, and combinationsthereof.

The coating composition of the present invention can be applied to asubstrate using any suitable procedure such as spray coating, rollcoating, coil coating, curtain coating, immersion coating, meniscuscoating, kiss coating, blade coating, knife coating, dip coating, slotcoating, slide coating, and the like, as well as other types ofpremetered coating. In one embodiment where the coating is used to coatmetal sheets or coils, the coating can be applied by roll coating.

The coating composition can be applied on a substrate prior to, orafter, forming the substrate into an article. In some embodiments, atleast a portion of a planar substrate is coated with one or more layersof the coating composition of the present invention, which is then curedbefore the substrate is formed into an article (e.g., via stamping,drawing, draw-redraw, etc.).

After applying the coating composition onto a substrate, the compositioncan be cured using a variety of processes, including, for example, ovenbaking by either conventional or convectional methods. The curingprocess may be performed in either discrete or combined steps. Forexample, the coated substrate can be dried at ambient temperature toleave the coating composition in a largely un-crosslinked state. Thecoated substrate can then be heated to fully cure the coatingcomposition. In certain instances, the coating composition can be driedand cured in one step. In preferred embodiments, the coating compositionof the present invention is a heat-curable coating composition.

The coating composition of the present invention may be applied, forexample, as a mono-coat direct to metal (or direct to pretreated metal),as a primer coat, as an intermediate coat, as a topcoat, or anycombination thereof.

Coating compositions of the present invention may be useful in a varietyof coating applications. The coating compositions are particularlyuseful as adherent coatings on interior or exterior surfaces of metalpackaging containers. Non-limiting examples of such articles includeclosures (including, e.g., internal surfaces of twist-off caps for foodand beverage containers); internal crowns; two and three-piece metalcans (including, e.g., food and beverage cans); shallow drawn cans; deepdrawn cans (including, e.g., multi-stage draw and redraw food cans); canends (including, e.g., riveted beverage can ends and easy open canends); monobloc aerosol containers; and general industrial containers,cans, and can ends.

The aforementioned coating composition is particularly well adapted foruse as a coating for two-piece cans, including two-piece cans having ariveted can end. Two-piece cans are manufactured by joining a can body(typically a drawn metal body) with a can end (typically a drawn metalend). The coatings of the present invention are suitable for use infood-contact situations and may be used on the inside of such cans. Thecoatings are also suited for use on the exterior of the cans. Notably,the present coatings are well adapted for use in a coil coatingoperation. In this operation a coil of a suitable substrate (e.g.,aluminum or steel sheet metal) is first coated with the coatingcomposition of the present invention (on one or both sides), cured(e.g., using a bake process), and then the cured substrate is formed(e.g., by stamping or drawing) into the can end or can body or both. Thecan end and can body are then sealed together with a food or beveragecontained therein.

In a preferred embodiment, the coating composition of the presentinvention is particularly well adapted for use as an internal orexternal coating on a riveted beverage can end (e.g., a beer or soda canend). Preferred embodiments of the coating composition exhibit anexcellent balance of corrosion resistance and fabrication properties(including on the harsh contours of the interior surface of the rivet towhich the pull tab attaches) when applied to metal coil that issubsequently fabricated into a beverage can end.

Some non-limiting embodiments are provided below to further illustratethe present invention.

A. A coating composition, comprising:

-   a copolyester resin preferably having a glass transition temperature    from 10° C. to 50° C. and the following structure:

(R¹)_(r)-([HARD]-X_(s)-[SOFT]-X_(s))_(n)—(R²)_(r)

wherein:

-   -   [HARD] independently denotes a hard segment preferably having a        Tg of from 10 to 100° C.,    -   [SOFT] independently denotes a soft segment,    -   each X, if present, is independently a divalent organic group,    -   s is 1,    -   n is 2 or more,    -   R¹, if present, is a reactive functional group, an organic        group, or a soft segment that optionally includes a terminal        reactive functional group or a divalent linkage group attaching        the soft segment to a hard segment,    -   R², if present, is a reactive functional group, an organic        group, or a hard segment that optionally includes a terminal        reactive functional group, and    -   each r is independently 0 or 1; and

-   a crosslinker;

-   wherein the coating composition is suitable for use as a    food-contact packaging coating when suitably cured; and

B. A coating composition that includes:

-   a copolyester resin preferably having a Tg from 10° C. to 50° C. and    including alternating hard and soft segments, wherein the    copolyester resin is a reaction product of ingredients including:    -   (i) a polyester oligomer or polymer preferably having a Tg from        10° C. to 100° C., and    -   (ii) an acid or diacid compound or equivalent (e.g., a        mono-carboxylic-functional compound, a di-carboxylic-functional        compound, an ester or anhydride equivalent thereof, or a mixture        thereof),    -   wherein the soft segments are provided by the acid or diacid        equivalent; and-   a crosslinker.

C. An article, comprising:

-   -   a food or beverage container, or a portion thereof, having a        metal substrate; and    -   a coating composition applied on at least a portion of the metal        substrate, wherein the coating composition includes:        -   a copolyester resin having a glass transition temperature            from 10° C. to 50° C. and the following structure:

(R¹)_(r)-([HARD]-X_(s)-[SOFT]-X_(s))_(n)—(R²)_(r)

-   -   -   -   wherein:                -   [HARD] independently denotes a hard segment,                -   [SOFT] independently denotes a soft segment,                -   each X, if present, is independently a divalent                    organic group,                -   each s is independently 0 or 1,                -   n is at least 2,                -   R¹, if present, is a reactive functional group, an                    organic group, or a soft segment that optionally                    includes a terminal reactive functional group or a                    divalent linkage group attaching the soft segment to                    a hard segment,                -   R², if present, is a reactive functional group, an                    organic group, or a hard segment that optionally                    includes a terminal reactive functional group, and                -   each r is independently 0 or 1; and

        -   a crosslinker.

D. A method, comprising:

-   -   providing a coating composition that is suitable for use as a        food-contact packaging coating when suitably cured, the coating        composition comprising:        -   a copolyester resin preferably having a Tg from 10° C. to            50° C. and the following structure:

(R¹)_(r)-([HARD]-X_(s)-[SOFT]-X_(s))_(n)—(R²)_(r)

-   -   -   -   wherein:                -   [HARD] independently denotes a hard segment,                -   [SOFT] independently denotes a soft segment,                -   each X, if present, is independently a divalent                    organic group,                -   each s is independently 0 or 1,                -   n is at least 1,                -   R¹, if present, is a reactive functional group, an                    organic group, or a soft segment that optionally                    includes a terminal reactive functional group or a                    divalent linkage group attaching the soft segment to                    a hard segment,                -   R², if present, is a reactive functional group, an                    organic group, or a hard segment that optionally                    includes a terminal reactive functional group,                -   each r is independently 0 or 1, and                -   the copolyester resin includes two or more hard                    segments; and

        -   a crosslinker; and

    -   applying the coating composition to at least a portion of a        planar metal substrate suitable for use in forming a food or        beverage container or a portion thereof.

E. A food or beverage container or a portion thereof formed from themethod of Embodiment D or having a coating composition of Embodiments Aor B applied on at least a portion of a major surface of a metalsubstrate.

F. Any of Embodiment A-E, wherein the hard segments are oligomersegments, polymer segments, or a combination thereof.

G. Any of Embodiments A-F, wherein the copolyester resin has a Tg from15 to 35° C. (prior to curing).

H. Any of Embodiments A-G, wherein the hard segments are derived from apolyester oligomer or polymer having a number average molecular weightof at least about 500.

I. Any of Embodiments A-H, wherein the hard segments have a Tg of from10° C. to 100° C.

J. Any of Embodiments A-I, wherein the soft segment comprises asubstituted or unsubstituted hydrocarbon segment having at least fourbackbone carbon atoms.

K. Any of Embodiments A-J, wherein the soft segment comprises a linearor branched hydrocarbon moiety that includes 6 to 36 carbon atoms.

L. Any of Embodiments A-K, wherein the soft segment is derived from acompound having the structure R³—(CR⁴ ₂)_(r)—R³, wherein: each R³ isindependently a reactive functional group capable of participating in astep-growth reaction (more preferably a carboxylic group); t is at least2, more preferably 4 to 60, even more preferably 6 to 36, and optimally8 to 36; and each R⁴ is independently a hydrogen, a halogen, or anorganic group.

M. Any of Embodiments A-L, wherein the soft segment is derived fromadipic acid, azelaic acid, a fatty-acid-based diacid, sebacic acid,succinic acid, glutaric acid, or a derivative or mixture thereof.

N. Any of Embodiments A and C-M, wherein s is 1 and X includes an esterlinkage.

O. Any of Embodiments A and C—N, wherein r is 1 and R¹ and R² are each areactive functional group.

P. Any of Embodiments A-O, wherein the copolyester resin is a reactionproduct of reactants including: a hydroxyl-functional polyester oligomeror polymer, and a diacid or diacid equivalent, wherein the weight ratioof polyester oligomer or polymer to diacid or diacid equivalent is from8:1 to 20:1.

Q. Any of Embodiments A-P, wherein the coating composition includes,based on total resin solids, at least 60 wt-% of the copolyester resin.

R. Any of Embodiments A-Q, wherein the coating composition furthercomprises from 2 to 20 wt-% of an acrylate copolymer that may optionallyinclude one or more glycidyl groups.

S. Any of Embodiments A-R, wherein the copolyester resin has one or bothof an acid number less than 10 or a hydroxyl number of from 10 to 50.

T. Any of Embodiments A-S, wherein the copolyester resin constitutesgreater than 90 wt-% of the total amount of polyester present in thecoating composition, based on total polyester solids.

U. Any of Embodiments A-T, wherein the coating composition issubstantially free of bound bisphenol A, and preferably substantiallyfree of both bound bisphenol A and aromatic glycidyl ether compounds.

V. Any of Embodiments C-U, wherein the article includes a rivetedbeverage can end having the coating composition applied on at least aportion of the can end.

W. Any of Embodiments A-V, wherein the coating composition, when presenton a riveted beverage can end at a dry film thickness of msi, passesless than 1 mA of current after being exposed for 4 seconds to aroom-temperature electrolyte solution containing 1% by weight of NaCldissolved in water.

Test Methods

Unless indicated otherwise, the following test methods were utilized inthe Examples that follow.

Differential Scanning calorimetry

Samples for differential scanning calorimetry (“DSC”) testing wereprepared by first applying the liquid resin composition or coatingcomposition onto aluminum sheet panels. For resin samples (e.g.,polyester oligomer or polymers used to form the hard segments or thefinal polyester polymer itself), the panels were then heated in a FisherIsotemp electric oven for 20 minutes at 300° F. (149° C.) to removevolatile materials. For coating composition samples, the panels werebaked for 12 seconds (total oven time) to a peak metal temperature of250° C. After cooling to room temperature, samples of film were scrapedfrom the panels, weighed into standard sample pans and analyzed usingthe standard DSC heat-cool-heat method. (If coating removal from thealuminum panels is overly difficult, glass panels may also be used.) Thesamples were equilibrated at −60° C., then heated at 1° C. per minute to200° C., cooled to −60° C., and then heated again at 1° C. per minute to200° C. Glass transitions points were calculated from the thermogram ofthe last heat cycle. The glass transition was measured at the inflectionpoint of the transition.

Water Retort and Pasteurization

These tests are a measure of the coating integrity of the coatedsubstrate after exposure to heat (and pressure in the case of waterretort) with a liquid such as water. Retort performance is notnecessarily required for all food and beverage coatings, but isdesirable for some product types that are packed under retortconditions. This test provides an indication of an ability of a coatingto withstand conditions frequently associated with food or beveragepreservation or sterilization. For the present evaluation, coatedsubstrate samples (in the form of flat panels) were placed in a vesseland partially immersed in water.

The water retort method was as follows: While partially immersed in thewater, the coated substrate samples were placed in an autoclave andsubjected to heat of 121° C. and pressure of 1 atm above atmosphericpressure for a time period of 90 minutes. Just after retort, the coatedsubstrate samples were tested for adhesion and blush resistance.

The water pasteurization method was as follows: Coated substrate samples(1.5 inches by 8 inches) were partially immersed in 82° C. distilledwater for 30 minutes. Just after water pasteurization, the coatedsubstrate samples were tested for adhesion and blush resistance.

Dowfax Detergent Test

The “Dowfax” test is designed to measure the resistance of a coating toa boiling detergent solution. The solution is prepared by mixing 1.96grams of DOWFAX chips (product of Dow Chemical) into one liter ofdeionized water. Typically, coated substrate strips are immersed intothe boiling Dowfax solution for 15 minutes. The strips are then rinsedand cooled in deionized water, dried, and then tested and rated forblush resistance and adhesion.

Solvent Resistance Test

The extent of “cure” or crosslinking of a coating is measured as aresistance to solvents, such as methyl ethyl ketone (MEK) or isopropylalcohol (IPA). This test is performed as described in ASTM D5402-93,with the exception that the cheesecloth was affixed to a 32-ounceball-peen hammer in order to apply constant pressure. The number ofdouble-rubs (i.e., one back-and-forth motion) before coating failure isreported, with rubbing ceased at 100 double-rubs if no coating failureis observed. Preferably, the MEK solvent resistance is at least 30double rubs.

Adhesion Test

Adhesion testing was performed to assess whether the coatingcompositions adhere to the underlying substrate. The Adhesion Test wasperformed according to ASTM D 3359—Test Method B, using SCOTCH 610 tape,available from 3M Company of Saint Paul, Minn. Adhesion is generallyrated on a scale of 0-10 where a rating of “10” indicates no adhesionfailure, a rating of “9” indicates 90% of the coating remains adhered, arating of “8” indicates 80% of the coating remains adhered, and so on. Acoating is considered herein to satisfy the Adhesion Test if it exhibitsan adhesion rating of at least 8.

Blush Resistance Test

Blush resistance measures the ability of a coating to resist attack byvarious solutions. Typically, blush is measured by the amount of waterabsorbed into a coated film. When the film absorbs water, it generallybecomes cloudy or looks white. Blush is generally measured visuallyusing a scale of 0-10 where a rating of “10” indicates no blush, arating of “8” indicates slight whitening of the film, and a rating of“5” indicates whitening of the film, and so on. Blush ratings of 7 ormore are typically desired for commercial packaging coatings andoptimally 9 or above.

Wedge Bend Test

This test provides an indication of a level of flexibility of a coatingand an extent of cure. For the present evaluation, test wedges wereformed from coated rectangular metal test sheets (which measured 12 cmlong by 10 cm wide). Test wedges were formed from the coated sheets byfolding (i.e., bending) the sheets around a mandrel. To accomplish this,the mandrel was positioned on the coated sheets so that it was orientedparallel to, and equidistant from, the 12 cm edges of the sheets. Theresulting test wedges had a 6 mm wedge diameter and a length of 12 cm.To assess the wedge bend properties of the coatings, the test wedgeswere positioned lengthwise in a metal block of a wedge bend tester and a2.4 kg weight was dropped onto the test wedges from a height of 60 cm.

The deformed test wedges were then immersed in a copper sulphate testsolution (prepared by combining 20 parts of CuSO₄.5H₂O, 70 parts ofdeionized water, and 10 parts of hydrochloric acid (36%)) for about 2minutes. The exposed metal was examined under a microscope and themillimeters of coating failure along the deformation axis of the testwedges was measured.

The results of this test for coatings prepared according to the presentinvention are expressed as a wedge bend percentage using the followingcalculation:

100%×[(120 mm)−(mm of failure)]/(120 mm)

A coating is considered herein to satisfy the Wedge Bend Test if itexhibits a wedge bend percentage of 70% or more.

Fabrication Test

This test measures the ability of a coated substrate to retain itsintegrity as it undergoes the formation process necessary to produce afabricated article such as a riveted beverage can end. It is a measureof the presence or absence of cracks or fractures in the formed end. Theend is typically placed on a cup filled with an electrolyte solution.The cup is inverted to expose the surface of the end to the electrolytesolution. The intensity of the current that passes through the end isthen measured. If the coating remains intact (no cracks or fractures)after fabrication, minimal current will pass through the end.

For the present evaluation, fully converted 202 standard openingbeverage ends were exposed for a period of 4 seconds to aroom-temperature electrolyte solution comprised of 1% NaCl by weight indeionized water. The coating to be evaluated was present on the interiorsurface of the beverage end at a dry film thickness of 6 to 7.5milligrams per square inch (“msi”) (or 9.3 to 11.6 grams per squaremeter), with 7 msi being the target thickness. Metal exposure wasmeasured using a WACO Enamel Rater II (available from theWilkens-Anderson Company, Chicago, Ill.) with an output voltage of 6.3volts. The measured electrical current intensity, in milliamps, isreported. End continuities are typically tested initially and then afterthe ends are subjected to pasteurization, Dowfax, or retort.

Preferred coatings of the present invention initially pass less than 10milliamps (mA) when tested as described above, more preferably less than5 mA, most preferably less than 2 mA, and optimally less than 1 mA.After pasteurization, Dowfax detergent test, or retort, preferredcoatings give continuities of less than 20 mA, more preferably less than10 mA, even more preferably less than 5 mA, and even more preferablyless than 1 mA.

EXAMPLES

The invention is illustrated by the following examples. It is to beunderstood that the particular examples, materials, amounts, andprocedures are to be interpreted broadly in accordance with the scopeand spirit of the inventions as set forth herein. Unless otherwiseindicated, all parts and percentages are by weight and all molecularweights are weight average molecular weight. Unless otherwise specified,all chemicals used are commercially available from, for example,Sigma-Aldrich, St. Louis, Mo.

Example 1 Polyester Polymers Having Hard and Soft Segments

The ingredients, and weights parts of each ingredient, used to producethe polyester copolymers of Example 1, Runs 1 and 2 are listed below inTable 1.

TABLE 1 Run 1 Run 2 Component (amount in grams) (amount in grams) 1 Monoethylene glycol 12 12 2 Neopentylglycol 101.9 101.9 3 Trimethylolpropane 13 13 4 Propylene glycol 30.7 30.7 5 Terephthalic acid 89.9 89.96 Isophthalic acid 156.9 156.9 7 Tin catalyst 0.7 — 8 Tin-free catalyst— 0.8 9 Dimer fatty acid 54.1 54.1 10 SOLVESSO 100 solvent 36.2 36.2 11Methoxy propyl acetate 292.3 292.3

The polyester polymers of Runs 1 and 2 were produced as described belowusing the same method.

A polyester polymer intermediate (corresponding to the hard segment) wasfirst produced from components 1-7 as follows. For each polyester,components 1 to 4 in Table 1 were added to a round-bottom flask equippedwith a stirrer, a partial-packed condenser topped with a decanter and atotal condenser, a thermometer, and a nitrogen feed. The temperature wasincreased to around 70° C. and maintained until the middle became fluid.Components 5 and 6 were then added slowly and the middle of the partialcondenser was heated to 110° C. before adding the catalyst (component7). The middle of the partial condenser was then progressively heated to245° C., while the temperature at the top of the partial condenser wasmaintained between 98° C. and 102° C. The temperature of the middle ofthe partial condenser was maintained at 245° C. to 250° C. until the cutviscosity at 55% non-volatile content (“NVC”) in ESTASOL solvent (amixture of dimethyl glutarate, adipate and succinate available from Dow)reached 21-23 Poises (Noury method) and the acid number was less than12. The water produced during the process (around 55 g) was removed fromthe equipment.

After cooling the polyester intermediate product and replacing thepartial condenser by a decanter topped with a total condenser,components 9 and 10 were added at 180° C. The mixture was maintained for30 minutes at a temperature of 175° C. The temperature was then slowlyincreased to maintain a gentle and continuous reflux. The reaction waterwas removed from the equipment via the decanter while the solvent wasreturned to the reaction vessel.

The mixture was cooled when the cut viscosity at 20° C. and 55% NVC in aDowanol PM (methoxy propanol)/Dowanol DPM (monoethyl ether ofdipropylene glycol) solvent mixture (3:1 mixture) reached 21-23 Poises(Noury method) and the acid number was less than 8. The temperature ofthe product was about 215° C. and the mass of collected reaction waterwas about 57 grams. At 160° C., component 11 was added to produce apolyester solution having the following characteristics: NVC (30 minutesat 180° C. for a 1 gram sample) was about 55%, the acid number (on dryresin) was less than 8, and the viscosity at 20° C. was 33-37 Poises(Noury method).

Example 2 Polyester Polymer Having Hard and Soft Segments

The polyester polymers of Example 2, Runs 3 and 4, were produced usingthe ingredients in the indicated weight parts listed below in Table 2.The process conditions and final composition parameters were similar tothat of Example 1.

TABLE 2 Run 3 Run 4 Components (amount in grams) (amount in grams) 1Methyl propane diol 243.37 243.4 2 Monoethylene glycol 39.4 39.4 3Cyclohexane dimethanol 59 59 (90% in water) 4 Trimethylol propane 7.97.9 5 Isophthalic acid 129.8 129.8 6 Terephthalic acid 380.4 380.4 7 Tincatalyst 1 0 8 Tin-free catalyst 0 0.96 9 Sebacic acid 129.8 129.8 10SOLVESSO 100 solvent 67.9 67.9 11 SOLVESSO 100 solvent 159 159 12 Xylene415 415

As described in the methodology of Example 1, a hydroxyl-terminatedpolyester polymer incorporating components 1-6 was first formed. Thereaction was continued until the intermediate polyester polymer productwas clear and the cut viscosity at 70% NVC in methoxypropyl acetatesolvent reached 40-45 Poises and the acid number was less than 7. Thehydroxyl-terminated polyester polymer intermediate was then reacted withsebacic acid (component 9) to form a polyester polymer having both hardand soft segments. The reaction was continued until the acid number wasless than 20. At 200° C., component 10 was added and the reflux wasmaintained until cut viscosity at 50% NVC in xylene solvent reached30-35 Poises at 25° C. A polyester solution was obtained after additionof components 11 and 12 having the following characteristics: aviscosity at 25° C. of 140-160 Poises, an acid number (on solids) ofless than 7, and a NVC (1 gram sample, 30 minutes at 150° C.) of 56-58%.

The polyester polymer of Example 2, Run 4 was determined to have a Tg of23° C.

Example 3 Coating Composition

The coating composition of Example 3 was prepared from the ingredientsusing the indicated weight parts listed in Table 3. The components belowwere added one-by-one and mixed together until a homogenous coatingsolution was obtained. The resulting coating composition, when cured,had a Tg of 31° C.

TABLE 3 Example 1, Run 2 Polyester 42.3 DOWANOL PMA methoxypropylacetate (Dow) 3.5 Xylene 8.8 Butylglycol 5.4 Amino crosslinker resin 7Acrylic resin* 3.9 Resole phenolic crosslinker resin 0.7 83X822catalyst** 0.3 Lubricant wax dispersion 1.9 SOLVESSO 100 aromatichydrocarbon solvent (Exxon) 13 DOWANOL PMA solvent 13 100 *The acrylicresin was an oxirane-functional acrylic resin formed from ingredientsincluding glycidyl methacrylate and had an Mn of 2,500 to 3,000 and aweight average molecular weight of 10,000 to 12,000. **The 83X822catalyst is a 10% solution of dodecylbenzenesulfonic acid in butanol,available from Cytec.

Example 4 Coated Article

The coating composition of Example 3 was applied using a hand bar coateron aluminum panel (0.22 mm thickness and having a conventional chromepre-treatment) to obtain a dry film weight of about 10 grams per squaremeter. The coated panel was cured for 12 seconds (total oven time) in asuitably heated oven so that a peak metal temperature of 240° C. wasachieved. The cured coating was then subjected to a variety of coatingevaluations to assess the coating properties of the cured film withrespect to use as a beverage end coating. These test results aresummarized in the below Table 4.

TABLE 4 Blush Adhesion Evaluation w/v* w/v* Water Pasteurization 10/1010/10 Dowfax Detergent Test  8/10 10/10 Water Retort 10/10 10/10Feathering (in millimeters) 0.1 after 45 minutes in 85° C. Water MEKdouble rubs 100 *“w” denotes data from portions of the coating exposedto the liquid phase and “v” denotes data from portions of the coatingexposed to the vapor phase.

The data reported in the above Table 4 is consistent with that of acoating composition suitable for use as an internal coating on a rivetedbeverage can end.

In addition, a cured coating composition identical to that of Example 3,except for that it included a different wax package, was evaluated usingthe Fabrication Test (after having been cured using cure conditionssimilar to that of Example 4). The cured beverage can end coatingpassed, on average, 0.11 mA of current.

Example 5 Coating Composition

A coating composition was prepared using the ingredients in theindicated amounts in the below Table 5. The components were addedone-by-one under agitation and mixed until the solution becamehomogeneous.

TABLE 5 Ingredient Amount (weight parts) Example 2, Run 2 Polyester 92Blocked isocyanate 17 Glycol-ether-type solvent 24 Additives (wax,wetting agent, etc.) 2

The viscosity of the resulting varnish was about 80 seconds (Number 4Ford cup at 20° C.) and the NVC (30 minutes at 180° C.) was about 40%.

Example 6 Coated Article

The varnish of Example 5 was applied as an overcoat varnish on asheet-fed-type panel of tin plate (0.20 millimeter thickness, 2.8 gramtin weight per square meter, 314 chrome treated) precoated with a whitebase coating (modified-polyester type coating). The dry film weight ofthe overcoat varnish was about 6 grams per square meter and the film wascured for 10 minutes (total oven time) in a 200° C. oven.

The resulting coated panel was then subjected to a variety of tests toassess the coating properties of the cured multi-coat coating system.The coating properties are reported in the below Table 6.

TABLE 6 Adhesion on ETP 10 Wedge Bend 100% MEK resistance >25 doublerubs

The coating properties data reported in the above Table 6 is consistentwith that of a coating composition suitable for use as a sheet-fed foodcan coating. In addition, the coating composition exhibited excellentscratch resistance/hardness (according to the Sheen test), which is animportant property for can production. The flexibility and the retortresistance in water were excellent and the coating composition exhibitedvery low thermal plasticity of the coating composition (as indicated byblocking resistance).

The complete disclosure of all patents, patent applications, andpublications, and electronically available material cited herein areincorporated by reference. The foregoing detailed description andexamples have been given for clarity of understanding only. Nounnecessary limitations are to be understood therefrom. The invention isnot limited to the exact details shown and described, for variationsobvious to one skilled in the art will be included within the inventiondefined by the claims.

What is claimed is:
 1. An article, comprising: a food or beveragecontainer, or a portion thereof, having a metal substrate; and a coatingcomposition applied on at least a portion of the metal substrate,wherein the coating composition includes: a copolyester resin having aglass transition temperature from 10° C. to 50° C. and the followingstructure:(R¹)_(r)-([HARD]-X_(s)-[SOFT]-X_(s))_(n)—(R²)_(r) wherein: [HARD]independently denotes a hard segment, [SOFT] independently denotes asoft segment, each X, if present, is independently a divalent organicgroup, each s is independently 0 or 1, n is at least 2, R¹, if present,is a reactive functional group, an organic group, or a soft segment thatoptionally includes a terminal reactive functional group or a divalentlinkage group attaching the soft segment to a hard segment, R², ifpresent, is a reactive functional group, an organic group, or a hardsegment that optionally includes a terminal reactive functional group,and each r is independently 0 or 1; and a crosslinker.
 2. The article ofclaim 1, wherein the hard segments are oligomer segments, polymersegments, or a combination thereof.
 3. The article of claim 1, whereinthe copolyester resin has a glass transition temperature from 15° C. to35° C.
 4. The article of claim 1, wherein the hard segments are derivedfrom a polyester oligomer or polymer having a number average molecularweight of at least about 500 and a glass transition temperature of from10° C. to 100°.
 5. (canceled)
 6. The article of claim 1, wherein thesoft segment comprises a substituted or unsubstituted hydrocarbonsegment having at least four backbone carbon atoms.
 7. The article ofclaim 1, wherein the soft segment comprises a linear or branchedhydrocarbon moiety that includes 6 to 36 carbon atoms.
 8. The article ofclaim 1, wherein the soft segment is derived from adipic acid, azelaicacid, a fatty-acid-based diacid, sebacic acid, succinic acid, glutaricacid, or a derivative or mixture thereof.
 9. The article of claim 1,wherein: s is 1, and X includes an ester linkage.
 10. The article ofclaim 9, wherein r is 1 and R¹ and R² are each a reactive functionalgroup.
 11. The article of claim 1, wherein the copolyester resin is areaction product of reactants including: a hydroxyl-functional polyesteroligomer or polymer, and a diacid or diacid equivalent, wherein theweight ratio of polyester oligomer or polymer to diacid or diacidequivalent is from 8:1 to 20:1.
 12. The article of claim 1, wherein thecoating composition includes, based on total resin solids, at least 60weight percent of the copolyester resin.
 13. The article of claim 1,wherein the coating composition further comprises, based on total resinsolids, from 2 to 20 weight percent of an acrylate copolymer.
 14. Thearticle of claim 13, wherein the acrylate copolymer includes one or moreglycidyl groups.
 15. The article of claim 1, wherein the copolyesterresin has an acid number less than 10 and a hydroxyl number of from 10to
 50. 16. (canceled)
 17. The article of claim 1, wherein thecopolyester resin constitutes greater than 90 weight percent of thetotal amount of polyester present in the coating composition, based ontotal polyester solids.
 18. The article of claim 1, wherein the coatingcomposition is substantially free of bound bisphenol A and aromaticglycidyl ether compounds.
 19. The article of claim 1, wherein thearticle includes a riveted beverage can end having the coatingcomposition applied on at least a portion of the can end.
 20. A method,comprising: providing a coating composition that is suitable for use asa food-contact packaging coating when suitably cured, the coatingcomposition comprising: a copolyester resin having a glass transitiontemperature from 10° C. to 50° C. and the following structure:(R¹)_(r)-([HARD]-X_(s)-[SOFT]-X_(s))_(n)—(R²)_(r) wherein: [HARD]independently denotes a hard segment, [SOFT] independently denotes asoft segment, each X, if present, is independently a divalent organicgroup, each s is independently 0 or 1, n is at least 1, R¹, if present,is a reactive functional group, an organic group, or a soft segment thatoptionally includes a terminal reactive functional group or a divalentlinkage group attaching the soft segment to a hard segment, R², ifpresent, is a reactive functional group, an organic group, or a hardsegment that optionally includes a terminal reactive functional group,each r is independently 0 or 1, and the copolyester resin includes twoor more hard segments; and a crosslinker; and applying the coatingcomposition to at least a portion of a planar metal substrate suitablefor use in forming a food or beverage container or a portion thereof.21. A coating composition, comprising: at least 60 weight percent, basedon total resin solids, of a copolyester resin having a glass transitiontemperature from 10° C. to 50° C. and the following structure:(R¹)_(r)-([HARD]-X_(s)-[SOFT]-X_(s))_(n)—(R²)_(r) wherein: [HARD]independently denotes a hard segment having a glass transitiontemperature of from 10° C. to 100° C., [SOFT] independently denotes asoft segment, each X, if present, is independently a divalent organicgroup, s is 1, n is 2 or more, R¹, if present, is a reactive functionalgroup, an organic group, or a soft segment that optionally includes aterminal reactive functional group or a divalent linkage group attachingthe soft segment to a hard segment, R², if present, is a reactivefunctional group, an organic group, or a hard segment that optionallyincludes a terminal reactive functional group, and each r isindependently 0 or 1; and a crosslinker; wherein the coating compositionis suitable for use as a food-contact packaging coating when suitablycured.
 22. The coating composition of claim 21, wherein the coatingcomposition, when present on a riveted beverage can end at a dry filmthickness of 7 milligrams per square inch, passes less than 1 milliampsof current after being exposed for 4 seconds to a room-temperatureelectrolyte solution containing 1% by weight of NaCl dissolved in water.23. (canceled)